Deck 3: Proteins I

Question 1

Which of the 20 standard amino acids is optically inactive?

A) Arg
B) Pro
C) Ile
D) Gly
E) Cys

Answer 1

Gly

Question 2

At a pH above its pK_a, the phenolic group of tyrosine is _____.

A) protonated and neutral
B) protonated and positively charged
C) deprotonated and neutral
D) deprotonated and negatively charged
E) none of the above

Answer 2

deprotonated and negatively charged

Question 3

At a pH above its pK_a, the $\varepsilon$ -amino group of lysine is _____.

A) protonated and neutral
B) protonated and positively charged
C) deprotonated and neutral
D) deprotonated and negatively charged
E) none of the above

Answer 3

protonated and positively charged

Question 4

At a pH above its pK_a, the R-group of Asp is _____.

A) protonated and neutral
B) protonated and positively charged
C) deprotonated and neutral
D) deprotonated and negatively charged
E) none of the above

Question 5

At pH 3, how many charged groups are present in the pentapeptide Ala-Asp-His-Ser-Lys?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 6

Which of the following structures shows the prevalent form of glutamic acid at pH 3?
A.
B.
C.
D.

A) a
B) b
C) c
D) d
E) none of the above

Question 7

Which of the following amino acids has a positively charged side chain at pH 7.4?

A) Glu
B) Ala
C) Lys
D) Leu
E) His

Question 8

Which of the following amino acids has a thiol group in its side chain?

A) Ser
B) Asn
C) Cys
D) Tyr
E) Met

Question 9

Serine has a _____ side chain; valine has a _____ side chain.

Question 10

Which of the following structures shows the prevalent form of histidine at pH 5?

A) a
B) b
C) c
D) d
E) none of the above

Question 11

Disulfide bonds form between two residues of which amino acid?

A) Met
B) Ser
C) Asn
D) Thr
E) Cys

Question 12

Leucine has a _____ side chain; glutamate has a _____ side chain.

Question 13

At physiological pH, all amino acids have at least _____ charged groups.

A) 0
B) 1
C) 2
D) 3
E) cannot be determined

Question 14

Which one of the representations describes the oligopeptide shown below?

A) Tyr-Ala-Thr
B) Tyr-Gly-Cys
C) Tyr-Ala-Ser
D) Phe-Gly-Cys
E) Phe-Ala-Thr

Question 15

When a peptide bond forms, an _____ reacts with a carboxylate group.

A) amide
B) amine
C) alcohol
D) ester
E) none of the above

Question 16

The formation of a dipeptide from two amino acids requires _____.

A) reduction of the $\alpha$ -carboxyl group
B) protonation of the $\alpha$ -amine group
C) interaction of the two side chains
D) loss of water
E) none of the above

Question 17

In the following figure, which bond would be unable to rotate?

A) a
B) b
C) c
D) d
E) none of the above

Question 18

Heme is considered a _____.

A) catalyst
B) prosthetic group
C) coenzyme
D) cofactor
E) none of the above

Question 19

Proteins such as hemoglobin are known as _____ proteins because binding of a molecule to one site alters binding to other sites.

A) ligand-activated
B) allosteric
C) induced-fit
D) cooperative
E) none of the above

Question 20

The amino acid _____ is commonly phosphorylated.

A) Ser
B) Asp
C) Asn
D) His
E) none of the above

Question 21

What level of protein structure is characterized by the amino acid sequence?

A) primary
B) secondary
C) tertiary
D) quaternary
E) none of the above

Question 22

The predominant noncovalent interaction seen in $\alpha$ helices and $\beta$ sheets is _____.

A) electrostatic interaction
B) hydrogen bond
C) dipole-dipole interaction
D) hydrophobic interaction
E) all of the above

Question 23

Which of the following amino acids is generally absent from an $\alpha$ helix?

A) Trp
B) Ser
C) Ile
D) Pro
E) none of the above

Question 24

Which of the following best describes the peptide backbone in a $\alpha$ sheet?

A) coiled
B) compacted
C) highly extended
D) rigid
E) none of the above

Question 25

Which of the following atoms would be considered a hydrogen-bond donor in an $\alpha$ helix?

A) a
B) b
C) c
D) d
E) none of the above

Question 26

The following is an example of _____.

A) parallel $\alpha$ helix
B) parallel $\beta$ sheet
C) antiparallel $\alpha$ helix
D) antiparallel $\beta$ sheet
E) none of the above

Question 27

The only observable regular secondary structures are $\alpha$ helices and $\beta$ sheets.

Question 28

Lysine can form a salt bridge by interacting with the side chain of _____.

A) Glu
B) Gly
C) Asn
D) Ser
E) Pro

Question 29

The side chain of serine could interact with the side chain of _____ using a(n) _____.

A) Val; hydrophobic interaction
B) His; hydrogen bond
C) Gln; hydrophobic interaction
D) Asn; electrostatic interaction
E) none of the above

Question 30

Which of the following interactions would be involved in quaternary structure?

A) hydrogen bonds
B) hydrophobic interactions
C) disulfide bonds
D) salt bridges
E) all of the above

Question 31

During the initial synthesis of collagen molecules, _____ and _____ are most often incorporated into the growing protein.

A) Ser; Gly
B) Pro; Ala
C) Gly; Pro
D) Ala; Gly
E) Ser; Pro